1. Field of the Invention
The invention relates to an electronic circuit technique, and particularly relates to a voltage regulator circuit and a control method for the voltage regulator circuit.
2. Description of Related Art
Recently, it has become the mainstream in the design of power circuits to apply a low-dropout regulator (LDO regulator) as a driving power in a switching pulse width modulation (PWM) voltage regulator. The LDO regulator has the advantages of low noise, small size, and low cost, and is broadly applied in the IC design of the PWM control chip in a direct current (DC) voltage regulator. The driving voltage of the PWM control chip needs to be stabilized at a predetermined level beforehand, so that voltage regulation and transistor switch control (e.g., the switch control of the metal oxide semiconductor field effect transistor (MOSFET)) in the PWM regulator may function normally. Therefore, it is common for the manufacturers of PWM control chips to adopt the LDO regulator to provide the driving power required for an internal PWM voltage regulator to drive a control circuit.
However, the input voltage source of the DC voltage regulator is normally directly adopted as the input source of the LDO regulator, but the input voltage level of the input voltage source may be as high as 24V or even higher. If the voltage value or other higher source voltages are directly adopted as the input source of the LDO regulator, the LDO regulator may have an excessive power loss due to a significant voltage different between the input and output ends of the LDO regulator. Therefore, the LDO regulator may overheat and be damaged easily, which may indirectly cause damage to the PWM control chip and make the PWM control chip no longer usable.
Besides, in some of the current designs, the output voltage of the voltage regulator is directly fed back as the input source of the LDO regulator. However, when the voltage regulator malfunctions due to overvoltage of output, the overvoltage of the output voltage may make the difference between the input and output voltages of the LDO regulator increase continuously due to continuous increase of the feedback voltage level. In the worst case, the LDO regulator may be damaged due to excessive power consumption caused by overvoltage, making the PWM control chip no longer usable. Therefore, how to reduce the voltage difference between the input and output of the LDO regulator, ensure the input source of the LDO regulator to be stable, so as not to be affected by the unexpected overvoltage that lasts, and reduce the power consumption of the LDO regulator are certainly issues that people skilled in the art should work on.